WASHINGTON – The House voted Thursday to give U.S. troops guaranteed time at home between deployments to Iraq, the latest but assuredly not the last challenge to President Bush from Democrats determined to end an unpopular war.

Bush threatened to veto the measure, which passed on a vote of 229-194. Six Republicans broke ranks to support it and three more voted “present” rather than take a firm position. Maine Democrat Rep. Tom Allen voted for the bill, stating: “We owe our troops more time to recover from the tremendous strain of deployment in Iraq and Afghanistan. … Repeated deployments and abbreviated rest periods at home have taken a tremendous toll.”

House Democrats staged the vote as Defense Secretary Robert Gates became the latest administration official to acknowledge miscalculations about Iraq and a national public opinion poll said support for a troop withdrawal exceeds 60 percent.

En route home from the Middle East, Gates acknowledged the slow pace of political reconciliation among Iraqi leaders. “In some ways we probably all underestimated the depth of the mistrust and how difficult it would be for these guys to come together,” Gates said.

The House measure would require that regular military units returning from the war receive at least as much time at home as they spent in Iraq. Reserve units would get a home stay three times as long as they spent in the war zone.

Under the Pentagon’s current policy, active duty troops typically serve deployments of up to 15 months, with a year at home in between. National Guard and Reserve ground units generally can be called for as long as two years, to be followed by six years at home.